Sanders are generally described by the characteristic motion by which drive their abrasive; sanders may be orbital, in-line, disk, or belt sanders. In-line, disk, and belt sanders gouge distinct abrading marks on the surface of the workpiece, by the cumulative effects of the abrading medium as it travels in the same direction. To produce a suitable finish, another tool, such as an orbital sander later must remove the resultant abrasion marks. Orbital sanders produce a more random abrading pattern, therefore, a more uniform and desirable surface finish. In general, using belt, inline, and disk sanders is limited to aggressive surface abrading of the workpiece surface.
Orbital sanders drive a sanding pad in an eccentric orbit around the motor shaft centerline. Operators prefer orbital sanders because of their controllability. When abrading a surface, an operator has excellent control of sander position, which is important because it allows the operator to abrade a precisely defined area, such as abrading next to masking tape or to a perpendicular surface. In contrast, belt, in-line, or disk, apply a reactionary force to the operator, opposite the direction of sanding medium motion. To keep such a sander in one location, the operator must always provide an equal reactionary force. As a result, belt, in-line, and disk sanders are more difficult to control.
Orbital sanders, however, generate relatively high vibration levels, up to 30 m/s2. With long exposures, these levels are often injurious to the operator, resulting in serious long-term nerve, vascular, or musculoskeletal damage of an upper extremity. The vibration is the result of imbalanced rotational forces along the shaft-assembly. These forces are dependent on operator pushing force as well as variations in counterweight mass, sanding pad mass, and sanding medium mass.
Orbital sanders have been limited in use to less aggressive abrading tool because of their vibration levels. A more aggressive orbital sander is one that swings its sanding pad at larger orbits that is with greater eccentricity rather than by increasing rotational speed. As a result, the sander drives the pad to abrade more area per orbit. The most aggressive orbital-sanders typically have ⅜-inch diameter orbits with rotational speeds between 10,000 and 12,000 orbits per minute.
Orbital sander manufacturers have not been able to design the vibration out of orbital sanders. The vibration results from imbalance, and in the design of orbital sanders, imbalance, in large part, stems from the displacement of a center of gravity from a center of rotation. Given the variety of weights of sandpapers, any replacement of sandpaper can offset the center of gravity from the center of rotation. Due to the varying weight of sandpaper, a single offset design is not possible.
The disadvantages associated with current orbital sanders have made it apparent that a new orbital sander that generates less vibration and is more aggressive is needed.